Snap action mechanism



April 5, 1938. 'r. G. RICHMOND SNAP ACTION MECHANISM Filed Oct. 22, 1935 2 Sheets-Sheet 1 April 5, 1938. T. G. RICHMOND 2,113,494

SNAP ACTION MECHANISM Filed Oct. 22, 1955 2 Sheets-Sheet 2 a a Rio/1m;

Patented Apr. 5, 1938 SNAP ACTION MECHANISM Thomas Guthrig Richmond, Glasgow, Scotland I Application October 22, 1935, Serial'No. 46,200 In Great Britain July 26, 1935 19 Claims.

This invention relates to snap action mechanism for operating electric switches, valves, or other devices.

In short-gap switches for handling ordinary commercial alternating currents or direct currents in conjunction with condensers large contacts are employed, and the quick snap action make-and-break is obtained by magnetic means.

One of the objects of the present invention is to provide a non-magnetic snap action mechanism for use with switches whereby very small differentials may be obtained.

Another object of this invention is to provide a non-magnetic snap action mechanism for electrical switches which will have a snap action in each direction and will permit of a very small gap being used between the contacts.

A further object of the invention is to provide a non-magneticsnap action mechanism for a thermostatically controlled gas valve.

Other objects of the invention will be apparent from the description to be hereinafter given.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a sectional view showing the device applied to a thermostat.

t Figure 2 is a side view of Figure 1 also in secion.

Figure 3 is a plan of Figure 1 with the top portion removed.

Figure 4 is a detail on an enlarged scale.

Figure 5 is a detail.

Figure 6 is a sectional view of a modification of 5 Figure 1.

Figure 7 is a sectional view of a further modification of Figure 1.

Figure 8 is a sectional view 01' the device applied to a tumbler switch.

40 Figure 9 is a sectional view of the device apcasing 2, but insulated therefrom by material [3,-

and is provided with an upstanding support 3 on one face of which a horizontal V groove 4 is provided, ,and inthisv groove is located an operatingf'member 5 which lies'substantially par allel to said. body, the operating member having a knife edge 6 at oneend parallel to said body about which itpivots in the V groove 4. .The

.55 lengthof the groovelis. approximately equal to the width of the operating member 5 so as to prevent it from moving sideways.

The other end of the operating member is provided with a contact I which engages with a fixed contact 8 mounted upon a suitable member 9 se- 5 cured to the body I by means of pillars ill, but insulated therefrom by suitable insulating means. This limits the movement in one direction. The contact 8 is preferably made adjustable in the member 9 and when set in the correct position 0 is locked therein -by the lock nut II. An adjustable stop l2, or the like, is provided upon the body I so as to limit the movement in the other direction and thus control the opening or gap between the contacts to any suitable amount. If 15 desired, the stop I2 may be mounted upon the operating member.

Provided upon the said body on the opposite end to the support 3 is another support I4 in which is situated a suitable screw or the like !5 having a cup or conical bearing I6 which may be jewelled if desired, or made of hardened steel or other suitable material. The operating member 5 is drilled longitudinally slightly offset of said knife edge 6 and the bottom of the hole is pro- 25 vided with a similar cup or conical bearing I'I which may be hardened steel or other material and pressed into position. A strut member l8 such as a. spring wire or the like is provided with conical pivot points, and this is fitted so that 30 one end rests in the bearing ll within the pivoted member and the other end in the bearing IS in the support; The screw I5 is then tightened up so that the strut member I8 keeps the operating member 5 in the V groove, and due to its pressure being ofl'set tends to turn the operating member about its knife edge and press the two contacts together. If desired, the strut member instead of being resilient may be made stifi and resiliency to press the strut member against 40 the operating member may be supplied by making either the support 3 or M resilient, or both. Further, all the three parts may be resilient, if desired. Also supported upon the pillars ill or the like is a spring member 20 having a Qepending tongue 2| or the like, which is arranged so that it will make contact with the strut member l8. This may be done by cutting a slot 22 in the operating member 5 between the contact and the knife edge so as to expose said strut member. This pressure is applied'to the strut member nearer to its fixed bearing l6 than to its movable bearing l1 so as to obtain the magnification.

,The thermally sensitive member comprises a brass tube 25 securely fixed at one end to the casing 2 and at the other end to a rod 26 which is a sliding fit in said casing. The rod 26 is connected rigidly to a stirrup member 21 which is provided with an adjusting screw 28 having a pointed end or tip 29 made of insulating material such, for

example, as glass or porcelain. This tip 29 is arranged to press against the spring member 20 so that its depending tongue 2| will press against the strut member [8 and thus apply a lateral force thereto which will overbalance the longitudinal pressure and. flick over the operating member 4 so that the contacts fly apart. spring member is arranged to magnify the movement of the means which applies the lateral force to the strut member. The energy to carry over the contact I is stored partly in the strut member I8 and partly in the spring member 20.

By turning the screw i5 which contains the bearing, the pressure on the longitudinal strut member i8 may be varied, and thus the distance through which the pointed end 29 and the de pending tongue must move to apply the necessary lateral pressure to the said strut member to cause the snap action is altered whereby the differential of the thermostat may be controlled. A knurled head 3|, having a pointer thereon, is provided upon the adjusting screw 28 so as to adjust the temperature at which the contacts open. A suitable scale or the like 32 is provided upon the top of the cover 33 which fits on to the casing 2 and encloses the instrument. Any other adjustable means may be provided-in any other suitable position, so as to adjust the temperature at which the contacts open.

carries the contact 8 and is secured to the body 23 by screws or the like. The arm 2| may have projecting lugs on each side which may be bent down to make contact with the stop below the strut member, or the stop may be bifurcated to pass round the strut member. Also a suitable hole may be made in the arm, which may be enlarged for the purpose, if necessary, for the tongue member 20 to pass therethrough.

According to a further form of the invention, as shown in Figure 6, the lateral pressure to cause the snap action is applied directly to the operating member 5 by the spring member 20, which is arranged so that it presses upon the operating member 5 close up to the knife edge 6 and in this manner magnification is also obtained. According to another form of the invention, as shown in Figure 7, the pressure for actuating the operating member 5 may be applied jointly both to the operating member and to the strut member. The spring 20 is arranged to press upon the strut member l8 near to its fixed bearing i6 and another spring member 35 is mounted upon the pillars I and is provided with an adjustable screw 31 which presses upon the end of the operating member having the knife edge 6. In this case, the strut member I8 may be given a considerable pressure by any suitable means and the screw member 31 applying the lateral pressure to the operating member is adjusted and locked in position so that the operating member is just on the balance; thus, when a very slight pressure is applied to the strut member by the thermally sensitive member, the operating member flicks over at once. By this method of applying jointly a lateral pressure both to the operating member and to the strut member a very fine differential is obtained and a very minute movement of the tongue member pressing against the strut member operates the mechanism. It will be seen that the pressure applied to the operating member is adjustable, but when once the differential is determined, this remains fixed and the pressure for actually operating the mechanism is applied to the tongue member 20 by the thermally sensitive or other member, whichever is used.

According to another form of the invention as applied to hand operated switches and as illustrated in Figure 8 the tumbler 40 of a tumbler switch is made to press up against the spring 20 so as to apply the lateral pressure to the operating member 5 and cause the contact 1 to flick over on to the stop I2 and break the circuit. The strut member l8 and other parts are the same as previously described with reference to the other examples. Suitable terminals are provided for connecting the contacts I and 8 to the current supply and the tumbler may be insulated from the spring 20 or the spring 20 may be insulated from the operating member 5. Directly the pressure is removed the contacts snap together and join the circuit.

In operation the device is so arranged that the strut member l8 in the normal position when the contacts I and 8 are closed holds them together by giving a clockwise moment, as shown in the Figures, about the knife edge, but when the strut member has a lateral pressure applied thereto which causes an anti-clockwise moment about the knife edge the clockwise moment is overbalanced and the anti-clockwise moment immediately snaps over the operating member with the contact I thus opening the circuit. Directly the lateral pressure is removed the clockwise moment again operates and the operating member snaps back 'to the normal position, closing the contacts automatically. Care must be taken that the parts are so arranged that the moment exerted by the strut on the operating member due to their being resiliently pressed together does not permanently alter its sign when the lateral pressure is applied, but returns to its original value and sign directly the pressure is released. In this manner the operating member automatically returns to its normal position. As long as this provision is made the pressure point or conical bearing on the operating member need not be offset from its longitudinal and the necessary moment may be created by the amount of bend or bow in the strut member.

The configuration of the parts is such that the longitudinal pressure exerted by the said resilient means acting upon the strut and operating members is always in a direction on the same side of the pivot point in both extreme positions of the operating member and thus the moment about the pivot point is always in the same direction. In order to obtain the snap action the parts must be so arranged that when the pressure applied to the strut member increases beyond a certain amount the equilibrium of the system is instantaneously upset, and the snap action takes place. The energy which causes the snap action to take place is stored in the resilient means exerting the longitudinal pressure or the resilient means applying the lateral pressure or both.

In this manner slight lateral pressure upon the strut member alters the direction of its moment and the operating member snaps over to the other extreme position. Directly the lateral pressure is removed, the moment, produced by the resilient means, snaps back the operating member to its other extreme position.

Further, the strut member instead of being made of a-simple straight wire which, under pressure, deforms into a bow, may be a compound member which, when given a longitudinal pressure, will deform symmetrically so as to apply the pressure to the operating member. In this case, when the strut member deforms symmetrically, it is necessary that the point of application of its pressure to the operating member be always offset, otherwise the mechanism will not automatically return to the normal position.

By choosing the distance between the knife edge and the point at which the longitudinal pressure is applied and also the amount of offset of this point from a line drawn through the V slot and the fixed conical bearing, various degrees of movement and magnification may be provided so that the contacts may either be used with short gap for alternating currents or with larger gaps for direct currents without the use of condensers.

A small movement of the member applying the lateral pressure creates a large movement at the end of the pivotal member, thus giving a large magnification.

Instead of applying pressure to the strut member by a thermally sensitive member any other means may be employed to apply a pressure such as a sensitive member controlled by pressure, or other hand operated means. If desired, this spring member having the depending tongue may be dispensed with and the thermally sensitive or other member may apply its force direct to said resilient strut member.

It is found desirable in certain circumstances where snap or quick action mechanism is employed for making or breaking circuits or other purposes, that the mechanism should not reset itself to the original position, or, in other words, that the mechanism should be tripped by some means or other, after which it is necessary that it be reset before it will automatically operate to snap or trip again.

The mechanism, according to the invention, is very suitable for this purpose and can be made to fulfil the requirements by arranging that the moment, which is applied to the operating member and which is overbalanced by the lateral applied force, reverses its sign on the trip action taking place, and therefore the operating member remains in its tripped position and does not return to the normal or reset itself.

According to one form as given by way of example and illustrated in Figure 9, as applied to a thermally operated switch mechanism as hereinbefore described, the strut member l8 and the operating member are so arranged that when the trip action takes place, they move from one position past thedead centre to another position, and carry the contact 1 against the stop 45. The moment created by the thrust of the strut member l8 reverses its sign when the operating. member has moved from one limiting position to the other. I

The stop 5 is mounted upon the end of the resetting lever Mi, which is pivoted at 41. When the switch has tripped the lever 46 is depressed to reset the operating member and close the contact, if conditions allow, so that they may be in a position to trip again when required.

In one example, for instance, in an electric kettle, a thermal device incorporating the above switch mechanism may be arranged to switch out the heating current should the kettle boil dry or no water he init, and the mechanism will not then automatically switch on until pressure is applied by hand to the resetting lever 46 to reset the operating member to the tripping position, which operation can only be carried out when the thermal element has cooled sufficiently.

The trip action mechanism may also be applied, for instance, to give an indication or an alarm when a certain temperature is reached, either by a rising or'by a falling temperature. In this case, the trip action moves the operating member to join the contacts and makes the circuit, thus causing the indication or alarm to be given when the temperature reaches the predetermined amount. The contacts remain together and the circuit closed until hand operated means are used to push the operating member back to its untripped position.

The thermally sensitive member in both cases trips the mechanism on reaching a predetermined temperature and the switch does not come back to the normal position unless reset by hand.

Various modifications and alterations in design of the operating member may be made, according to the functions it has to perform. For instance, it may have two or more contacts for double or multiple pole working mounted thereon, in which case it may take the form somewhat of a U, and the resilient means would then be situated between the two arms of the U.

If desired, it might also take the shape of an L, the short arm of which receives the longitudinal pressure of the strut member, and the long arm of which would actuate the required device.

Further, when the mechanism is used in an electric switch, acontact on each side of the operating member may be provided, if desired, so that in both extreme positions electrical contact is made or broken. The movement may be limited in the position when the contacts are open by the operating member itself coming in contact with the strut member in the case in which the strut member is contained within a hole or slot in said operating member.

Suitable means, of course, are provided where necessary, for insulating the various members, and suitable terminals are provided for connecting to leads.-

The pivot point of the operating member is provided with a knife edge to reduce friction and make it very sensitive, and this also applies to the anti-friction bearing of the strut member.

It is to be understood that the snap action mechanism may be employed for other purposes than thermostats and may be used for operating switches, and further, that they may be applied to oher devices than switches, such as gas valves used in connection with thermostats, or in other devices in which a small movement is required to be magnified to give a large movement of the operating member with snap action for actuating the desired mechanism, and can thus be applied to any devices for which it is suitable.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:-

1. A snap action make and break mechanism comprising in combination a body, a non-resilient operating member pivoted at one end to said body, a member at the other end of said body, with which the other end of said operating member makes contact, a member pivotally supported at one end on said body and at the other end on said operating member applying a resilient turning moment to said operating member in one direction, means for applying a resilient force to said operating member to create a turning moment in the opposite direction, movement of said operating member taking place when one turning moment overbalances the other turning moment, the snap action being due to the overbalanced turning moment decreasing more rapidly than the other turning moment, and means to prevent said operating member passing through the dead centre or neutral position.

2. A snap action make and break short gap mechanism, comprising in combination, a body, two upstanding supports on said body, a nonresilient operating member pivotally supported at one end on one of said supports, a floating member pivotally supported upon said operating member and said other support applying a resilient turning moment in one direction, a member on said body, a member on said operating member contacting with said body member, means for preventing said operating member passing through dead centre or neutral position when the contacting members are opened, a resilient member mounted upon said body and pressing upon said operating member applying a turning moment in the opposite direction, and means coacting with said resilient member to apply pres-. sure thereto.

3. A snap action make and break short gap switch comprising in combination a body, two upstanding supports on said body, a non-resilient operating member pivotally supported at one end on one of said supports, a floating member pivotally supported upon said operating member and said other support applying a. resilient turning moment in one direction, a contact on said body, a contact on said operating member engaging with said body contact, means for preventing said operating member passing through dead centre or neutral position when the contacts are opened, resilient means mounted upon said body for applying a turning moment to said operating member in the opposite direction, and means coacting with said resilient member to apply pressure thereto.

4. A snap action make and break short gap thermostatic switch comprising in combination, a body, two upstanding supports on said body, a non-resilient operating member pivotally supported at one end on one of said supports, a floating member pivotally supported upon said operating member and said other support applying a resilient turning moment in one direction, a contact on said body, a contact on said operating member engaging with said body contact,

means for preventing said operating memberpassing through dead centre or neutral position when the contacts are opened, resilient means mounted upon said body for applying a turning moment to said operating member in the opposite direction, and a thermally sensitive member coacfiing with said resilient member to apply pressure thereto.

5.-A snap action make and break short gap thermostatic switch comprising in combination, a body, two upstanding supports on said body, a none-resilient operating member pivotally supported at one end on one of said supports, a floating member engaging with said body contact,

means for preventing said operating member passing through dead centre or neutral position when the contacts are opened, a resilient member mounted upon said body and pressing upon said operating member applying a turning moment in the opposite direction, and a thermally sensitive member coacting with said resilient member to apply pressure thereto.

6. A snap action make and break mechanism comprising in combination a body, an operating member pivoted at one end to said body, a member at the other end of said body, with which the other end of said operating member makes con tact, a member pivotally supported at one end on said body and at the other end on said operating member applying a resilient turning moment to said operating member in one direction, and a resilient member mounted upon said body adapted to apply a force which creates a turning moment which is applied in the opposite direction to said operating member, movement of said operating member taking place when one turning moment overbalances the other turning moment,

, and the snap action being due to the overbalanced other turning moment and taking place before the I said operating member reaches the dead centre or neutral position.

'I. A snapaction make and break short gap mechanism, comprising in combination, a body, two upstanding supports on said body, an operating member pivotally supported at one end on one of said supports, a floating member pivotally supported upon said operating member and said other support applying a resilient turning moment in one direction, a member on said body, a member on said operating member contacting with said body member, a resilient member mounted upon said body adapted to apply a force which creates a turning moment which is applied in the opposite direction to said operating member, and means coacting with said resilient member to apply pressure thereto, said snap action taking place before the said operating member reaches the dead centre or neutral position.

8. A snap action make and break short gap switch comprising in combination a body, two upstanding supports on said body, a non-resilient operating member pivotally supported at one end on one of said supports, a floating member pivotally supported upon said operating member and said other support applying a'resilient turning moment in one direction to said operating member, means for adjusting the end pressure on said floating member, a contact on said body, a contact on said operating member engaging with said body contact, means for preventing said operating member passing through dead centre or neutral position when the contacts are opened, a resilient member mounted upon said body and pressing upon said operating member applying a turning moment in the opposite direction, and

means coacting with said resilient member to apply pressure thereto.

9. A snap action make and break short gap thermostat comprising abody, two upturned supports provided upon said body, a non-resilient operating member, two pivoting means provided upon said operating member, one of said pivoted means engaging one of said supports, a floating member engaging between said other pivotal means and said other support for keeping said operating member in engagement with said support and applying a turning moment in one direction, a contact upon said body, a contact upon said operating member coacting with said body contact, means for preventing said operating member passing through dead centre or neutral position when the contacts are opened, a resilient member mounted upon said body and pressing upon said operating member, a second resilient member mounted upon said body and pressing upon said floating member forapplying a turning moment in the opposite direction and a thermally sensitive member coacting with said second resilient member to apply pressure thereto.

10. A snap action make and break short gap switch comprising in combination a body, two

supports on said body, a non-resilient operating member pivotally supported at one end on one of said supports, a floating member pivotally supported upon said operating member and said other support applying a resilient turning moment in one direction, a contact on said body, a contact on said operating member engaging with said body contact, means for preventing said operating member passing through dead centre or neutral position when the contacts are opened, a resilient member mounted upon said body and pressing upon said operating, member applying a turning moment in the opposite direction, and manually operated means coacting with said resilient member to apply pressure thereto.

11. A snap action make and break short gap switch comprising in combination, a body, two upstanding supports on said body, a non-resilient operating member pivotally supported at one end on one of said supports, a floating member pivotally supported upon said operating member and said other support applying a resilient turning moment in one direction, a contact on said body, a contact on said operating member engaging with said body contact, means for preventing said operating member passing through dead centre or neutral position when the contacts are opened, a resilient member mounted upon said body, and pressing upon said floating member and means applying a turning moment in the opposite direction coacting with said resilient member to applypressure thereto.

12. A snap action make and break short gap switch comprising in combination, a body, two upstanding supports on said body, a non-resilient operating member pivotally supported at one end on one of said supports, a floating member pivotally supported upon said operating member and said other support applying a resilient turning moment in one direction, a contact on said body, a contact on said operating member engaging with said body contact, means for preventing said operating member passing through dead centre or neutral position when the contacts are opened, a resilient member mounted upon said body and pressing upon said floating member, and manually operated means coacting with said resilient member to apply pressure thereto.

13. A snap action make and break short gap thermostatic switch as claimed in claim 4, in which the resilient turning moment is created by making the floating member resilient.

14. A snap action make and break short gap thermostatic switch comprising in combination, a body, two upstanding supports on said body, a non-resilient operating member pivotally sup- 2 ported at one end on one of said supports, a

floating member pivotally supported upon said operating member and said other support applying a resilient turning moment in one direction, a contact on said body, a contact on said operating member engaging with said body contact, a resilient member mounted upon said body and pressing upon said operating member applying a turning moment in the opposite direction, a thermally sensitive member coacting with said resilient member to apply pressure thereto, and means permitting said operating member passing through dead centre or neutral position after said snap action has taken place.

15. A snap action make and break short gap switch comprising in combination, a body, two upstanding supports on said body, a non-resilient operating member pivotally supported at one end on one of said supports, a floating member pivotally. supported upon said operating member and said other support applying a resilient turning moment in one direction, means for adjusting the end pressure on said floating member, a contact on said body, a contact on said operating member engaging with said body contact, means for preventing said operating member passing through dead centre or neutral position when the contacts are opened,a resilient member mounted upon said body and pressing upon said floating member, and means applying a turning moment in the opposite direction coacting with said resilient member to apply pressure thereto.

16. A snap action make and break short gap thermostat comprising a body, two upturned supports provided upon said body, a non-resilient operating member, two pivoting means provided upon said operating member, one of said pivoted means engaging one of said supports, a floating member engaging between said other pivotal means and said other support for keeping said operating member in engagement with said support and applying a turning moment in one direction, means for adjusting the end pressure on said floating member, a contact on said body, a contact upon said operating member coacting with said body contact, means for preventing said operating member passing through dead centre or neutral position when the contacts are opened, a resilient member mounted upon. said body and pressing upon said operating member, means for adjusting the pressure with which the resilient member presses upon the operating member, a second resilient member mounted upon 'said body and pressing upon said floating member for applying a turning moment in the opposite direction and a thermally sensitive member coacting with said second resilient member to apply pressure thereto.

17. A snap action make and break short gap switch comprising in combination, a body, twoupstanding supports on said body, a V groove in one support, a cup shaped bearing in the other said support, a non-resilient operating member, aknife edge on said operating member engaging said V groove on said support, a cup shaped bearing on said operating member, a floating member supported in said cup bearings on the support and operating member respectively, said floating member applying a resilient turning moment in one direction to said operating member, means for adjusting the force exerted by said-floating member upon said operating member, a contact on a portion of said operating member remote from the two bearings, a contact on said body adapted to be engaged by said contact on said operating member, a stop to limit the gap between the contacts and to prevent the operating member from passing through dead centre or neutral position, a resilient member mounted upon said body to press upon said operating member for applying a turning moment in the opposite direction, and means coacting with said resilient member to apply pressure thereto.

18. A snap action make and break short gap switch comprising in combination,-a body, two upstanding supports on said body, a V groove in one support, a cup shaped bearing in the other said support, a non-resilient operating member, a knife edge on said operating member engaging said V groove on said support, a cup shaped bearing on said operating member, a floating member supported in said cup bearings on the support and operating member respectively, said floating member applying a resilient turning moment in one direction to said operating member, means for adjusting the force exerted by said floating member upon said operating member, a contact on a portion of said operating member remote from the two bearings, a contact on said body adapted to be engaged by said contact on said operating member, a stop to limit the gap between the contacts and to prevent the operating member from passing through dead centre or neutral position, a resilient member mounted upon said body to press upon 'said floating member for applying a turning moment in the opposite direction, and means coacting with said resilient member to apply pressure thereto.

19. A snap action make and break short gap thermostatic switch, comprising in combination, a body, two upstanding supports on said body, a non-resilient operating member pivotally supported atone end on one of said supports, a floating member pivotally supported upon said operating member and said other support applying a resilient turning moment in one direction, a contact on said body, a contact on said operating member engaging with said body contact,

means for preventing said operating member pass-:

ing through dead centre or neutral position when the contacts are opened, a resilient member mounted upon said body and pressing upon said floating member applying a turning moment in the opposite direction, and a thermally sensitive member coacting with said resilient member to apply pressure thereto.

THOMAS GUTHRIG RICHLIOND. 

